Contrast-enhanced three-dimensional magnetic resonance angiography (3DMRA) is proving to be a useful diagnostic adjunct to x-ray angiography. However, spatial resolution is currently inferior to that afforded by x-ray angiography, which is one reason why MRA has not generally replaced x-ray angiography. The applicants have recently developed a method for increasing spatial and/or temporal resolution without increasing gradient demands. The method is called SMASH (SiMultaneous Acquisition of Spatial harmonics) and is based on obtaining spatial information simultaneously through traditional phase encoding as well as by independent sampling of signals from the radiofrequency coil elements in a multicoil array. The methodology permits an acceleration in data acquisition rate by a factor as large as the number of elements in the multicoil array. The applicants propose to develop and test the SMASH technique for CE-3DMRA in two clinically vital vascular systems: the extracranial carotid and renal arteries. They intend to obtain at least a four-fold, and potentially up to an eight-fold acceleration of the data acquisition rate. The acceleration will allow corresponding improvements in spatial or temporal resolution. The specific aims of this proposal are: 1. To develop multicoil arrays suitable for imaging of the extracranial carotid and renal arteries. 2. To evaluate SMASH CE-3DMRA using an ameroid-occluder pig model of renal artery stenosis. 3. In patients, using x-ray angiography as the correlative gold standard: a) To determine if SMAS, by improving spatial resolution of CE-3DMRA of the extracranial carotid arteries, enhances the accuracy of measurements of stenoses compared with conventional CE-#DMRA. B) To determine if SMASH can be used to reduce the scan time for CE-3DMRA of the renal arteries, while maintaining equal image quality compared with conventional CE-3DMRA, or alternatively, to see of SMASH, by improving the spatial resolution of renal artery CE-3DMRA, enhance the accuracy of measurements of stenoses compared with conventional CE-3DMRA.